Now methods for realizing short-distance communications of a mobile phone have emerged, by adding radio-frequency functions to the SIM (Subscriber Identity Module) card of the mobile phone (called radio-frequency SIM card), adding radio-frequency function to the TF (T-Flash, also called MicroSD) card of the mobile phone (called radio-frequency TF card), or adding short-distance communication modules to the main board of the mobile phone. The emergence of such methods makes a mobile phone a super smart terminal that can recharge, consume, transact, and authenticate an identity, greatly meeting the urgent demand of the market.
Among those, the mobile phone short-distance solution based on radio-frequency SIM/TF is given extensive attention for its advantages such as simplicity and no need to change existing mobile phones. In this solution, technologies such as UHF (Ultra High Frequency) are adopted in the radio-frequency SIM/TF so that the radio-frequency signal can still be transmitted from a mobile phone when the radio-frequency SIM/TF card is inserted in the mobile phone. In this way, the existing mobile phone can possess short-distance communication functions, without changing any structure of the mobile phone. The transmission effects of radio-frequency signal of different mobile phones, however, vary greatly due to the differences between mobile phones' internal structures. For a mobile phone with strong transmission, the radio-frequency communication distance of the radio-frequency SIM/TF card can reach a few meters. Even for a mobile phone with weak transmission, the communication distance of the radio-frequency SIM/TF card can also reach dozens of centimeters. In mobile payment applications, such as card swiping in a public transit subway, usually there are strict requirements for a transaction distance to ensure the safety of the transaction. For example, the transaction distance is limited below 10 centimeters to avoid any loss due to mistaken card swiping when the user does not know. On the other hand, it is also required to ensure the communication reliability by limiting the transaction distance within a specified distance, to improve the transaction efficiency. Therefore, for radio-frequency SIM/TF based mobile phones, while short-distance communication functions are added to them, the ranges of their transaction distances must be effectively controlled.
Therefore, a system and method combining short-distance communication with low-frequency alternating magnetic field and RF high-frequency communication are provided to resolve the above problems. This system uses a low-frequency alternating magnetic field to realize distance detection and control, and to realize one-way communication between a card reader and a SIM/TF card. The system also uses a RF channel combining with low-frequency communication to realize a reliable binding with a terminal. Meanwhile, it uses a RF channel to realize high-speed data communication between the card reader and the card. In this solution, however, how to realize the low-frequency signal detection and the transmission system in the SIM/TF card influences the accuracy of the distance detection and control. Therefore, how to realize low-frequency signal detection and a transmission system in a SIM/TF card, especially how to realize a magnetic induction module in a SIM/TF card, is one of the problems to be resolved currently.